The present invention relates to a brake apparatus that provides a braking force to a vehicle such as an automobile.
As brake apparatuses mounted on vehicles such as automobiles, there are known brake apparatuses equipped with an electric parking brake function actuated (actuated to hold a braking force and actuated to release a braking force) based on driving of an electric motor. Such brake apparatuses are configured to, for example, advance a pressing member by the electric motor, and hold the advanced pressing member by a pressing member holding mechanism, thereby succeeding in maintaining a frictional member (a pad or a shoe) in abutment with a rotational member (a disk or a drum) on a wheel side (maintaining the braking force applied to the vehicle).
On the other hand, parking the vehicle for a long time results in reductions in temperatures of the disk rotor (the rotational member) and the brake pad (the frictional member) that were heated according to, for example, application of a braking force while the vehicle is running, thereby reducing thermal expansion amounts of the disk rotor and the brake pads (causing to the disk rotor and the brake pads to thermally contract). Japanese Patent Application Public Disclosure No. 2012-192874 (hereinafter referred to as Patent Literature 1) discusses a brake apparatus configured to set a zero point position, based on which a brake pad is displaced, in consideration of a reduction in a thermal expansion amount of a disk rotor, when an ignition is turned on. More specifically, Patent Literature 1 discusses that, when the ignition is turned on, the brake apparatus estimates a present temperature of the disk rotor with use of a time period elapsed since the ignition was turned off last time, which is measured by a timer, and an ambient temperature, and calculates the thermal expansion amount based on this estimated temperature.
The conventional technique discussed in Patent Literature 1 requires power to be supplied to the timer for measuring the elapsed time period to calculate the thermal expansion amount even after the ignition is turned off. Therefore, if the vehicle is configured to stop the timer (stop power supply to the timer) at the same time when the ignition is turned off, the brake apparatus cannot correctly calculate the thermal expansion amount, and therefore may be unable to provide an appropriate thrust force (braking force).